Variable displacement engine (VDE) designs can provide increased fuel efficiency by deactivating cylinders during operational modes with decreased engine output. Such designs may incorporate cylinder deactivation valve control (CDVC) hardware for deactivating the cylinders. As one example, the CDVC hardware may include a cam profile switching (CPS) system that uses a solenoid actuated by a current driver to switch to a no-lift cam profile for deactivating cylinder intake and exhaust valves, and thus the corresponding cylinder. However, a current drawn by the CDVC solenoid is a function of solenoid impedance, which is a function of solenoid temperature. At lower solenoid temperatures, the effective solenoid impedance may be so low that the potential current drawn by the solenoid is greater than a capability of the current driver, which may cause current driver degradation. Therefore, the CDVC hardware may not be actuated during conditions when the solenoid temperature is expected to be low, such as during an engine cold start. For example, a control system may model the solenoid impedance to estimate when CDVC solenoid actuation is enabled, with a conservative bias to avoid over-current. As another example, the control system may use a timer to prevent CDVC solenoid actuation until the engine has been on for a predetermined duration to ensure that the CDVC solenoid has been warmed through engine operation. As a result, CDVC solenoid actuation may be delayed.
Other attempts to reduce CDVC solenoid actuation time include operating the solenoid at a low level prior to the actuation. One example approach is shown by Doering et al. in U.S. Pat. No. 9,657,611 B2. Therein, the solenoid is operated at a lower pre-charge or pre-activation level in response to an increased potential for a valve transition (e.g., due to an expected transition into or out of a VDE operating region). Then, in response to the transition to the VDE operating region, the level is increased to a maximum level to quickly actuate the solenoid for the valve transition.
However, the inventors herein have recognized potential issues with such systems. As one example, expediting valve transitions while the engine is cold is not addressed, as the increased potential for the valve transition includes operating with an engine temperature above a threshold temperature for valve transitions. The inventors herein have recognized that systems and methods that provide a direct measurement of the CDVC solenoid condition may enable sooner CDVC solenoid actuation without risking over-current, thereby enabling faster transitions to the VDE mode of operation after engine start for increased fuel savings.
In one example, the issues described above may be addressed by a method comprising: while operating an engine in a first condition, sending a lower command signal to a cylinder deactivation valve control (CDVC) system without actuating a cylinder valve transition; determining an impedance of a solenoid of the CDVC system while sending the lower command signal; and actuating the cylinder valve transition responsive to the determined impedance by sending a higher command signal to the CDVC system. In this way, a condition of the solenoid may be accurately monitored so that the cylinder valve transition may be performed as soon as the risk of over-current is mitigated.
As one example, while operating the engine in a second condition, the cylinder valve transition may be actuated by sending the higher command signal to the CDVC system without first sending the lower command signal. For example, the first condition may correspond to an engine cold start condition, and the second condition may correspond to a warm engine condition. Thus, the CDVC system may be operated with the lower command signal when the solenoid is expected to be cold in order to avoid exceeding a current driver capacity, whereas the valve transition may be performed (e.g., via the higher command signal) when the solenoid is expected to be warm enough that over-current will not occur. As another example, the impedance of the solenoid may be determined based on a current consumed by the solenoid while sending the lower command signal. For example, the current consumed by the solenoid while sending the lower command signal may be determined via a current sensing circuit, thus providing a direct measurement of the solenoid condition.
Further, in order to determine if the solenoid condition enables actuation, the determined impedance may be used to estimate an expected current consumption by the solenoid at the higher command signal. Then, if the expected current draw is less than or equal to a threshold current, the actuation may be performed by operating the CDVC system at the higher command signal. The threshold current may be at or near the current driver capacity, for example. On the other hand, if the expected current draw is greater than the threshold current, the actuation will not be performed, as over-current is expected. Instead, the CDVC system may again be operated at the lower command signal to further increase a temperature of the solenoid, and thus increase the impedance and decrease the current draw at a given command signal. Further, the lower command signal may be increased to expedite solenoid warming while remaining below the higher command signal, thus avoiding actuation. In this way, the valve transition may be enabled faster than if the solenoid is only warmed through engine operation, and the risk of over-current is mitigated.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.